They way I interpret David's question is how valuable is it to know the "objective" truth. In other words (this is pertinent example I see him asking), someone believes in G-d and because of that acts in a more ethical way then he otherwise would. If we could somehow show him that he is infact wrong and that G-d doesn't exist should we? We know that the pre-suppositions of his entire life are wrong but they result in "Advantageous" behavior.

Is their an intrinsic value to knowing the truth or being right (if the knowing said truth causes you harm)?

IMO no. I see absolutely zero value in being right. I would give up nothing.